These secretions are carried by blood and/or lymph to the target organ. On the other hand an exocrine gland secretes material directly into the duct. They have their own ducts which carry the secretions directly to the target organ.

Characteristics of Hormones:

i. Hormones are regulatory chemicals which are secreted by endocrine glands directly into the blood.

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ii. They are produced in very minute quantity

iii. They are biologically very active and their action is very rapid.

iv. They act only on target organs or cells located usually away from their sources.

v. They regulate the physiological process of the body by bringing about chemical changes. Thus, they bring about metabolic regulation in the body.

vi. They are destroyed soon after their action and thus not stored in the body.

Two Main Categories of Hormones:

Steroid Hormones:

They are steroid in nature. They diffuse through the cell membrane and bind to internal receptors. Examples: Oestrogen, progesterone, androgens, Cortisol, aldosterone, thyroid hormones, etc.

Peptide or Non-Steroidal Hormones:

These are amino acid derivatives, peptides or proteins. They bind to receptors located on the surface of target cell. Examples: Glucagons, ADH, Oxytocin, Insulin, Somatotropin, Prolactin, FSH, LH, TSH, etc.

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